MIL-DTL-13924 Rev. D

Downloaded from http://www.everyspec.com
NOT MEASUREMENT
SENSITIVE
MIL-DTL-13924D
18 March 1999
SUPERSEDING
MIL-C-13924C
9 June l980
DETAIL SPECIFICATION
COATING, OXIDE, BLACK, FOR FERROUS METALS
This specification is approved for use by all Departments
and Agencies of the Department of Defense.
1.
SCOPE
1.1 Scope. This specification covers black oxide coatings applied to ferrous
metals (wrought iron, carbon, low alloy, and corrosion resistant steels). Black
oxide coatings, with or without a supplementary preservative treatment (see 3.11),
may be used where a black surface is required. Only very limited corrosion
protection, under mildly corrosive conditions, is obtained as a result of black
oxide coating (see 6.1). Black coatings are included in this specification with
limitations as noted in 1.2.
1.2 Classification. Black oxide coatings covered by this specification should be
of the following classes as specified (see 6.2 and 6.3.2).
Class 1
Alkaline oxidizing process (for wrought iron, cast and malleable
irons, plain carbon, and low alloy steels).
Class 2
Alkaline chromate oxidizing process (for use on certain corrosion
resistant steel alloys which are tempered at less than 900°F (482°C)).
Class 3
Fused salt oxidizing process (for corrosion resistant steel alloys
which are tempered at 900°F (482°C) or higher).
Class 4
Alkaline oxidizing process (for other corrosion resistant steel
alloys).
Beneficial comments (recommendations, additions, deletions) and any pertinent data
which may be of use in improving this document should be addressed to: Director,
U.S. Army Research Laboratory, Weapons and Materials Research Directorate,
ATTN: AMSRL-WM-M, Aberdeen Proving Ground, MD 21005-5069 by using the
Standardization Document Improvement Proposal (DD Form 1426) appearing at the end
of this document or by letter.
AMSC N/A
AREA MFFP
Downloaded from http://www.everyspec.com
MIL-DTL-13924D
2.
APPLICABLE DOCUMENTS
2.1 General. The documents listed in this section are specified in sections 3
and 4 of this specification. This section does not include documents in other
sections of this specification or recommended for additional information or as
examples. While every effort has been made to ensure the completeness of this list,
document users are cautioned that they must meet all specified requirements
documents cited in sections 3 and 4 of this specification, whether or not they are
listed.
2.2
Government documents.
2.2.1 Specifications, standards, and handbooks. The following specifications,
standards, and handbooks form a part of this document to the extent specified
herein. Unless otherwise specified, the issues of these documents are those listed
in the issue of the Department of Defense Index of Specifications and
Standards(DoDISS) and supplement thereto, cited in the solicitation (see 6.2).
SPECIFICATIONS
DEPARTMENT OF DEFENSE
MIL-C-53072
Chemical Agent Resistant Coating (CARC) System Application
Procedures And Quality Control Inspection
(Unless otherwise indicated, copies of the above specifications, standards, and
handbooks are available from the Defense Automated Printing Service (DAPS), Building 4D,
700 Robbins Avenue, Philadelphia, PA 19111-5094).
2.3 Non-Government publications. The following documents form a part of this
document to the extent specified herein. Unless otherwise specified, the issues of
the documents which are DoD adopted are those listed in the issue of the DoDISS cited
in the solicitation. Unless otherwise specified, the issues of documents not listed
in the DoDISS are the issues of the documents cited in the solicitation (see 6.2).
AMERICAN SOCIETY FOR TESTING AND MATERIALS (ASTM)
ASTM B117
Operating Salt Spray (Fog) Apparatus
(DoD adopted)
ASTM F519
Mechanical Hydrogen Embrittlement Testing of Plating Processes
and Aircraft Maintenance Chemicals
(Application for copies should be addressed to the American Society for Testing and
Materials, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959.)
SOCIETY OF AUTOMOTIVE ENGINEERS, INC. (SAE)
AMS 2759/9
Hydrogen Embrittlement Relief (Baking) Of Steel Parts
(Application for copies should be addressed to the Society Of Automotive
Engineers, Inc., 400 Commonwealth Drive, Warrendale, PA 15096.)
2.4 Order of precedence. In the event of a conflict between the text of this
document and the references cited herein, the text of this document takes
precedence. Nothing in this document, however, supersedes applicable laws and
regulations unless a specific exemption has been obtained.
2
Downloaded from http://www.everyspec.com
MIL-DTL-13924D
3.
REQUIREMENTS
3.1 Materials. The materials for the blackening processes shall be selected by
the contractor. The selected materials shall result in black coatings meeting all
the applicable requirements of this specification.
3.2 Preparation of basis metal. Prior to the application of the black coatings,
the basis metal shall be thoroughly cleaned. The cleaned surfaces shall be free of
rust, scale, grease, oil, paint, or other foreign matter, and shall pass the water
break test described in MIL-C-53072. Cleaning materials and methods shall be at the
option of the contractor. The cleaning process shall be performed without
measurable abrasion or erosion.
3.2.1 Stress relief. Unless otherwise specified for a particular end item
specification or drawing, after forming and hardening, and prior to cleaning and
coating, objectionable residual stress in ferrous alloy parts having a hardness
greater than 40 HRC shall be relieved by suitable heat treatment. The temperature
shall be such that maximum relief is given without hardness being reduced to less
than the specified minimum. Stress relief is not necessary where it has been
demonstrated that coating has no harmful effect on the coated part.
3.2.2 Coating as a final process. Unless otherwise specified, the black coatings
shall be applied after all machining, forming, welding, cold straightening and heat
treatment have been completed.
3.3
Application of black coatings. The coating shall conform to the class
specified. The specified black coating shall be applied under controlled time and
temperature conditions. All equipment together with solutions or baths shall be
properly maintained and kept free of dirt or possible contaminants. The selected
process shall not reduce the hardness of the parts being processed or expose the
parts to temperatures in the temper brittle range of the material, nor shall it
cause embrittlement of the steel.
3.3.1 Surface attack. The process shall not result in any attack of the surface,
either pitting or intergranular.
3.4 Alkaline oxidizing solutions (classes 1 and 2). Classes 1 and 2 oxide coatings
shall be formed from a boiling alkaline oxidizing or alkaline chromate oxidizing
solution, respectively.
3.4.1
water.
Rinsing.
All classes of black oxide coated pieces shall be rinsed in cold
3.4.2 Chromic acid dip. After the cold water rinse (see 3.4.1) the pieces shall
be dipped for a minimum of 30 seconds in a 0.06 percent solution (8 oz. chromic acid
per 100 gallons water) of chromic acid maintained at a temperature of l50 to l90°F
(66 to 88°C) and a pH of 2 to 3. After the chromic acid dip, parts shall be dried
without further rinsing by using warm dry air.
3.5 Fused salt oxidizing (class 3). The temperature of the molten oxidizing salt
of class 3 shall not be higher than 900°F (482°C). After suitable immersion, the
treated parts shall be withdrawn, cooled from eight to ten minutes and rinsed in hot
water, l90°F (88°C), followed by thorough cold water rinsing to effect complete
removal of blackening solution. After rinsing, the parts shall be dried by warm dry
air and given a chromic acid dip as outlined in 3.4.2.
3
Downloaded from http://www.everyspec.com
MIL-DTL-13924D
3.6 Alkaline oxidizing (class 4). The black coating of class 4 shall be
processed in accordance with instructions furnished by the suppliers of the raw
materials and the resulting coating shall conform to the applicable requirements of
this specification.
3.7 Coverage and color. Class 1, 2, 3, and 4 coatings
basis metal completely and shall pass the smut test. The
black. A slight amount of smut, which is inherent in the
cause for rejection. There shall be no indication of any
smut when tested as in 4.4.1. Smut "spottiness" shall be
unsatisfactory requiring reprocessing.
(see 1.2) shall cover the
color shall be a uniform
process, shall not be
reddish-brown or green
classified as
3.8 Oxalic acid spot test (class 1, 2, and 3). The black oxide coatings of
classes 1, 2, and 3, prior to the application of a preservative, shall pass the
oxalic acid spot test for a good quality coating (figure 3) as specified in 4.4.2.
3.9 Resistance to salt spray (fog) (class 4 AISI type 300 series corrosion
resistant steel only). The black coating, of class 4 (300 series only), prior to
the application of a preservative, shall show no signs of corrosion after 96 hours
of exposure in the salt spray test (see 4.4.3).
3.10 Hydrogen embrittlement relief treatment. Steel parts that are surface or
through hardened at 40 HRC and above shall be given a hydrogen embrittlement relief
treatment after application of the oxide coating. Coated springs or other parts
subject to flexure shall not be flexed prior to the embrittlement relief treatment.
If an embrittlement relief treatment is required, it shall follow the chromic acid
rinse. The embrittlement relief treatment precedes the supplementary preservative
treatment.
3.11 Supplementary preservative. Materials for supplementary preservative
treatments and methods of application shall be in accordance with the applicable
requirements of the end item specification, or as otherwise specified. Unless
otherwise specified, the supplementary preservative treatment shall be applied to
the clean and dry parts immediately after the final stage of processing.
3.12 Workmanship. The surface of the coated part shall be uniform in appearance
and free of visible coating defects, such as blisters, pits, roughness, nodules,
burning, cracks, or uncoated areas, and other defects that will affect the function
of the coating. The coated parts shall be clean and free of damage.
4.
VERIFICATION
4.1 Responsibility for inspection. Unless otherwise specified in the contract or
purchase order, the contractor is responsible for the performance of all inspection
requirements (examinations and tests) as specified herein. Except as otherwise
specified in the contract or purchase order, the contractor may use his own or any
other facilities suitable for the performance of the inspection requirements
specified herein, unless disapproved by the Government. The Government reserves the
right to perform any of the inspections set forth in this specification where such
inspections are deemed necessary to ensure supplies and services conform to
prescribed requirements.
4
Downloaded from http://www.everyspec.com
MIL-DTL-13924D
4.1.1 Classification. All the tests required for the testing are classified as
quality conformance tests, for which necessary sampling techniques and the methods
of testing are specified in this section.
4.2
Sampling.
4.2.1 Lot. A lot shall consist of coated parts of the same class, same basis
metal, and approximately the same size and shape and coated under similar
conditions. A maximum of 8 hours continuous production shall constitute a lot.
4.2.2 Selection. The number of random samples selected for nondestructive tests
(visual inspection, coverage, color, smut, and workmanship), and destructive tests
(oxalic acid spot test, salt spray test, and embrittlement relief test) from each
lot of coated parts shall be defined by the procuring activity (see 6.2).
4.3 Acceptance and rejection. The selected coated parts shall meet the
requirements in this specification for the represented lot to be acceptable.
Failure of any test samples to meet the requirements in this specification shall
constitute rejection of the entire lot which they represent. Unless otherwise
specified (see 6.2), the tests shall be conducted and the test results accepted
prior to shipment of the lot of coated parts represented by the test samples.
4.3.1 Surface attack. Parts shall be examined for pitted surfaces or
intergranular attack by viewing them at magnifications up to 10x.
4.4
Test procedures.
4.4.1 Smut test. The test shall be made prior to application of corrosion
preventive compound or after vapor degreasing. Each black oxide coated piece shall be
inspected visually under strong light to assure a satisfactory appearance. Each
sample shall also be wiped with a clean white cloth for indications of smut (see 3.7).
A slight amount of smut which is inherent in the process is acceptable for all classes
of coatings and shall not be cause for rejection.
4.4.2 Oxalic acid spot test (class 1, 2, and 3). The black oxide coated pieces of
classes 1, 2, and 3 only, prior to the application of a preservative, shall be handled
with clean cotton gloves or the equivalent. Each sample shall have deposited, on one
flat spot of the black oxide coated surface, three drops (0.00676 oz. (0.2 ml)) of a
five percent solution of oxalic acid. The reaction shall be observed after 30 seconds
and up to eight minutes. After eight minutes the panel shall be rinsed and compared
to figures 1, 2, and 3. A light gray center with a lighter border color (figure 1)
indicates a poor quality coating. A gray-black center with a light border (figure 2)
indicates a borderline quality coating. The coating shall conform to the good quality
coating of figure 3 to be acceptable. A black or dark brown center with a light
border (figure 3) indicates a good quality coating. A good quality coating may show a
light border, indicating exposure of metal around the drops. Parts shall therefore be
judged only on the color and exposure of the metal under the drops.
4.4.3 Resistance to salt spray (class 4). The coated pieces of class 4
(AISI type 300 series corrosion resistant steel) shall be subjected to a 5 percent
salt spray (fog) test in accordance with ASTM B117. Exposure time for the black
coatings, prior to the application of a preservative, or after vapor degreasing,
shall comply with the requirements of 3.9.
5
Downloaded from http://www.everyspec.com
MIL-DTL-13924D
4.4.4 Hydrogen embrittlement relief treatment. When specified (see 6.2), ferrous
parts shall be baked in accordance with AMS 2759/9, table 1.
4.4.4.1 Hydrogen embrittlement relief test. Samples selected in accordance with
4.2.2 to determine the adequacy of the hydrogen embrittlement relief treatment,
shall be tested in accordance with ASTM F519. When specified (see 6.2), the
standard notched round bar specimen under load control described in annex A1, which
is a part of ASTM F519, shall be used. The lot shall be rejected if any coated
specimen develops any crack or fails by fracture as a result of the test.
5.
5.1
6.
PACKAGING
Packaging.
Packaging requirements are not applicable to this specification.
NOTES
(This section contains information of a general or explanatory nature that may be
helpful, but is not mandatory.)
6.1 Intended use. The black oxide coatings covered by this specification are
military unique. Black oxide coatings are used on munition cases and gun barrels.
These coatings are particularly suited for moving parts that cannot tolerate the
dimensional build up of a more corrosion resistant finish. They are not recommended
on parts going into long term storage. Sometimes, long term storage is required and
a protective preservative fluid is recommended or a desiccated package is utilized.
The coatings present a pleasing black appearance frequently employed for decorative
purposes or decrease in light reflection. A supplementary water displacing
preservative coating such as MIL-PRF-16173, grade 3 or comparable material which
will provide equal or superior corrosion protection may be specified.
CAUTION:
6.2
High strength steel (40 HRC or greater hardness)
may be subjected to "caustic embrittlement" that could
lead to spontaneous cracking if under internal or applied
stress during the blackening treatment.
Acquisition requirements.
Acquisition documents should specify the following:
(a) Title, number, and date of this specification.
(b) Class of coating (see 1.2).
(c) Issue of DoDISS to be cited in the solicitation, and if required, the
specific issue of individual documents referenced (see 2.2.1 and 2.3).
(d) Number of samples to be inspected from the lot of coated parts (see 4.2.2).
(e) Acceptance requirements prior to shipment of the coated parts, if
different (see 4.3).
(f) Bake ferrous parts in accordance with AMS 2759/9, table 1 (see 4.4.4).
(g) Use the standard notched round bar specimen under load control described
in annex A1, which is a part of ASTM F519 (see 4.4.4.1).
6.3
Miscellaneous notes.
6.3.l Dimensional change. Black oxide coatings on iron and steel should produce
no appreciable dimensional change of the treated piece. The dimensions shown on the
drawings are, therefore, the dimensions after the application of the coatings.
6
Downloaded from http://www.everyspec.com
MIL-DTL-13924D
6.3.2 Processing. Contractors may employ one of a number of trade name black
finishing oxidizing materials or prepared chemical mixtures to apply the black oxide
coating. The processing details should conform to MIL-HDBK-205, “Phosphatizing and
Black Oxide Coating of Ferrous Metals”, or as recommended by the material supplier.
Class 2 is used to process the 4XX series corrosion resisting steels, class 3 is
used for 3XX and 4XX series, and class 4 is used to process those 300 series
corrosion resisting steels which can meet the special salt spray test criteria and
for those 4XX series corrosion resisting steels which do not have any special salt
spray test criteria. Table I provides an outline of the various processes.
6.3.3 Cast and malleable irons, and certain 400 series corrosion resistant
steels. Cast and malleable irons and 400 series corrosion resistant steels of the
martensitic type can also be effectively treated in Class 4 proprietary baths, but
will not meet the salt spray requirement of austenitic 300 series corrosion
resistant steels.
6.3.4 Class 4 coatings. Corrosion resisting steels of minimum composition
l7Cr-7Ni can be effectively blackened by this process.
6.3.5 Rinsing. In order to obtain effective removal of blackening solution and
ensure thorough rinsing, a combination of spray rinses with tank rinses or a
properly operated double counterflow rinse operation may be advantageous. Use of
such a system may help reduce the amount of water required to obtain a desired
rinsing criterion and facilitate meeting the EPA standard.
6.3.6 Ozone depleting chemicals. Classes I and II ozone depleting chemicals
should be avoided when cleaning the basis metal.
6.3.7 Hazardous materials. The DoD has put together a list of hazardous or
environmentally damaging substances in a document called the SD-14. These chemicals
should be avoided whenever another finish can be substituted for the finish
specified herein.
6.4
Subject term (key word) listing.
Chromic acid dip
Chromium compounds
Embrittlement relief
Oxalic acid spot test
Preservative
Salt spray
Smut test
6.5 Changes from previous issue. Marginal notations are not used in this
revision to identify changes with respect to the previous issue due to the
extensiveness of the changes.
7
Downloaded from http://www.everyspec.com
MIL-DTL-13924D
CONCLUDING MATERIAL
Custodians:
Army - MR
Navy - OS
Air Force - 11
Preparing activity:
Army - MR
(Project MFFP-0664)
Review activities:
Army - MI, PT
Navy - AS, EC, SH
Air Force - 13, 19
DLA - DH(DCMC-OF, DLSC-LEQ)
8
Downloaded from http://www.everyspec.com
MIL-DTL-13924D
TABLE I.
Materials and processing procedures.
____________________________________________________________________________________
Process and
Approximate
Approximate
Applicability to
possible
processing
immersion
Class
ferrous metals
chemicals
temperature
time
____________________________________________________________________________________
1
Carbon steels,
Alkaline
1 or 2
5 to 60 min.
low alloy steels,
oxidizing,
tanks
wrought irons,
NaOH,
boiling at
cast and malleable
NaNO3,
285 - 305°F
irons
water
(141 - 152°C)
____________________________________________________________________________________
Certain corrosion
Alkaline
250°F ± 10°F
30 to 45 min.
resistant steel
chromate
(121°C ± 5°C)
alloys which are
NaOH, NaNO3,
tempered at
Na2Cr207 1/,
less than 482°C
Water
____________________________________________________________________________________
2
3
For corrosion
Fused salt
Molten bath
30 min.
resistant steel
oxidizing
750 - 850°F
alloys which
Na2Cr207 1/
(399 - 454°C)
are tempered at
and/or
900°F (482°C)
K2Cr207 1/
or higher
____________________________________________________________________________________
4
Alkaline
250 - 265°F
15 to 30 min.
oxidizing,
(121 - 130°C)
proprietary
compounds
plus water
____________________________________________________________________________________
1/
For corrosion
resistant
steel alloys
Chromium compounds.
9
Downloaded from http://www.everyspec.com
MIL-DTL-13924D
OXALIC ACID SPOT TESTS ON BLACK OXIDE COATINGS
A poor quality coating.
FIGURE 1.
A borderline quality
coating.
A good quality coating.
FIGURE 2.
FIGURE 3.
10
Downloaded from http://www.everyspec.com
STANDARDIZATION DOCUMENT IMPROVEMENT PROPOSAL
INSTRUCTIONS
1.
The preparing activity must complete blocks 1, 2, 3, and 8. In block 1, both the document number and revision letter should be
given.
2.
The submitter of this form must complete blocks 4, 5, 6, and 7.
3.
The preparing activity must provide a reply within 30 days from receipt of the form.
NOTE: This form may not be used to request copies of documents, nor to request waivers, or clarification of requirements on current
contracts. Comments submitted on this form do not constitute or imply authorization to waive any portion of the referenced
document(s) or to amend contractual requirements.
I RECOMMEND A CHANGE:
DOCUMENT TITLE
1.
DOCUMENT NUMBER
2. DOCUMENTDATE (YYMMDD)
990318
MIL-DTL-13924D
COATING, OXIDE, BLACK, FOR FERROUS METALS
4. NATURE OF CHANGE
(Identify paragraph number and include proposed rewrite, if possible. Attach extra sheets as needed.)
5. REASON FOR RECOMMENDATION
6. SUBMITTER
a. NAME (Last, First, Middle Initial)
b. ORGANIZATION
c. ADDRESS (Include Zip Code)
d. TELEPHONE (Include Area Code)
(1) Commercial
7.DATE SUBMITTED
(YYMMDD)
(2) AUTOVON
(if applicable)
8. PREPARING ACTIVITY
a. NAME
b. TELEPHONE Include Area Code)
(1) Commercial
410-306-0725
US ARM RESEARCH LABORATORY
c. ADDRESS (Include Zip Code)Commander
WEAPONS AND MATERIALS RESEARCH DIRECTORATE
ATTN; AMSRL-WM-M
ABERDEEN PROVING GROUND, MD 21005-5069
DD Form 1426, OCT 89
(2) AUTOVON
458-0725
IF YOU DO NOT RECEIVE A REPLY WITHIN 45 DAYS, CONTACT:
DEFENSE QUALITY AND STANDARDIZATION OFFICE
5203 Leesburg Pike, Suite 1403, Falls Church, VA 22401-3466
Telephone (703) 756-2340
AUTOVON 289-2340
Previous editions are obsolete.
198/290